全文获取类型
收费全文 | 6558篇 |
免费 | 400篇 |
国内免费 | 1148篇 |
专业分类
化学 | 4579篇 |
晶体学 | 37篇 |
力学 | 360篇 |
综合类 | 75篇 |
数学 | 1223篇 |
物理学 | 1832篇 |
出版年
2024年 | 21篇 |
2023年 | 123篇 |
2022年 | 190篇 |
2021年 | 144篇 |
2020年 | 182篇 |
2019年 | 160篇 |
2018年 | 149篇 |
2017年 | 212篇 |
2016年 | 226篇 |
2015年 | 188篇 |
2014年 | 304篇 |
2013年 | 438篇 |
2012年 | 349篇 |
2011年 | 445篇 |
2010年 | 348篇 |
2009年 | 483篇 |
2008年 | 441篇 |
2007年 | 527篇 |
2006年 | 429篇 |
2005年 | 348篇 |
2004年 | 310篇 |
2003年 | 275篇 |
2002年 | 233篇 |
2001年 | 212篇 |
2000年 | 170篇 |
1999年 | 178篇 |
1998年 | 150篇 |
1997年 | 147篇 |
1996年 | 115篇 |
1995年 | 93篇 |
1994年 | 82篇 |
1993年 | 59篇 |
1992年 | 60篇 |
1991年 | 46篇 |
1990年 | 41篇 |
1989年 | 35篇 |
1988年 | 37篇 |
1987年 | 16篇 |
1986年 | 25篇 |
1985年 | 16篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1966年 | 1篇 |
排序方式: 共有8106条查询结果,搜索用时 62 毫秒
31.
Adsorption process of methylchloride (CH3Cl) on the GaAs (0 0 1)-2 × 4 surface was studied by a scanning tunnelling microscopy (STM) measurement. The arsenic rich 2 × 4 surface, which was prepared by molecular beam epitaxy (MBE), was exposed to a supersonic molecular beam of CH3Cl with a kinetic energy of 0.06 eV. New bright spots appeared on the CH3Cl exposed surface. They were largely observed at the “B-type” step edge and divided into two types according to their locations. It was suggested that new spots were due to weakly adsorbed CH3Cl molecules without any dissociation. The adsorption mechanism of CH3Cl molecule was also studied by an ab initio Hartree-Fock calculation, which explained the experimental results well. 相似文献
32.
33.
结合2006年全国大学生数学建模竟赛D题,借助Matlab软件,通过数学建模,计算出有关煤矿瓦斯和煤尘的3个主要安全指标,从而为解决煤矿实际安全生产提供了参考. 相似文献
34.
David Loffreda 《Surface science》2006,600(10):2103-2112
Adsorption thermodynamics based on density functional theory (DFT) calculations are exposed for the interaction of several multifunctional molecules with Pt and Au(1 1 0)-(1 × 2) surfaces. The Gibbs free adsorption energy explicitly depends on the adsorption internal energy, which is derived from DFT adsorption energy, and the vibrational entropy change during the chemisorption process. Zero-point energy (ZPE) corrections have been systematically applied to the adsorption energy. Moreover the vibrational entropy change has been computed on the basis of DFT harmonic frequencies (gas and adsorbed phases, clean surfaces), which have been extended to all the adsorbate vibrations and the metallic surface phonons. The phase diagrams plotted in realistic conditions of temperature (from 100 to 400 K) and pressure (0.15 atm) show that the ZPE corrected adsorption energy is the main contribution. When strong chemisorption is considered on the Pt surface, the multifunctional molecules are adsorbed on the surface in the considered temperature range. In contrast for weak chemisorption on the Au surface, the thermodynamic results should be held cautiously. The systematic errors of the model (choice of the functional, configurational entropy and vibrational entropy) make difficult the prediction of the adsorption-desorption phase boundaries. 相似文献
35.
对线性模型参数,讨论了Bayes估计的Pitman最优性,将已有结果进行了改进,去掉了附加条件,证明了在Pitman准则下,Bayes估计一致优于最小二乘估计(LSE),在此基础上,提出了一种基于先验信息的方差分量估计,通过和基于LSE的方差分量估计作比较,证明了新估计是无偏估计且有更小的均方误差.最后,证明了在Pitman准则下生长曲线模型参数的Bayes估计优于最佳线性无偏估计. 相似文献
36.
Y. Fukuda T. Kobayashi H. Yoshida T. Sekizawa N. Sanada 《Applied Surface Science》2002,190(1-4):279-283
Adsorption and decomposition of triethylindium (TEI: (C2H5)3In) on a GaP(0 0 1)-(2×1) surface have been studied by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). It is found from the TPD result that ethyl radical and ethylene are evolved at about 300–400 and 450–550 K, respectively, as decomposition products of TEI on the surface. This result is quite different from that on the GaP(0 0 1)-(2×4) surface. The activation energy of desorption of ethyl radical is estimated to be about 93 kJ/mol. It is suggested that TEI is adsorbed molecularly on the surface at 100 K and that some of TEI molecules are dissociated into C2H5 to form P–C2H5 bonds at 300 K. The vibration modes related to ethyl group are decreased in intensity at about 300–400 and 450–550 K, which is consistent with the TPD result. The TEI molecules (including mono- and di-ethylindium) are not evolved from the surface. Based on the TPD and HREELS results, the decomposition mechanism of TEI on the GaP(0 0 1)-(2×1) surface is discussed and compared with that on the (2×4) surface. 相似文献
37.
HU Yun & SHEN Yuliang Department of Mathematics Suzhou University Suzhou China 《中国科学A辑(英文版)》2006,(7)
We will be mainly concerned with some important fiber spaces over Teichmuller spaces, including the Bers fiber space and Teichmuller curve, establishing an isomorphism theorem between "punctured" Teichmuller curves and determining the biholomorphic isomorphisms of these fiber spaces. 相似文献
38.
Hu Haiyan 《Acta Mechanica Solida Sinica》1994,7(2):137-150
This paper deals with the numerical solution of high dimensional dynamic systems with nonsmooth characteristics, such as structural elastoplasticity, mechanical clearance and dry friction. As a stable periodic response of the system attracts its transient response, it may be extracted from the transient response somehow. The paper suggests a novel iteration scheme to extrapolate the periodic response from a short time history of its transient response by curve fitting. Compared with the current schemes such as shooting and incremental harmonic balancing, the present scheme makes full use of the information within the transient response and the system characters, then its computation efficiency has increased by an order and the numerical convergence depending on the initial iteration has greatly improved.The subject supported by the Chinese Foundation of Aeronautical Science 相似文献
39.
40.
František Toman Ludvík Beneš 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(3-4):231-236
Differential molar adsorption enthalpies (DMAE) were determined by gas chromatographic measurements of specific retention
volume of vapors on the surface of two forms of Mg–Al hydrotalcite. A linear dependence of the DMAE on the number of the carbon
atoms in hydrocarbons was observed for both form of hydrotalcite. The dependence of the differential molar adsorption enthalpies
on the number of chlorine atoms in organic molecules is discussed. A linear dependence of DMAE on the molecular weight of
chloroderivatives of methane and ethylene on the basic form in an order monochloromethane < dichloromethane < trichloromethane
or vinylidene chloride < 1,1-dichloroethylene < trichloroethylene was found. 相似文献